Tibial implant for a knee prosthesis

ABSTRACT

A tibial implant for knee prosthesis has a tibial socket (1) accepting a tibial plate (2) notably in polyethylene. The tibial socket (1) has a recess (1a) with a shape and section chosen to allow, from the upper face of said socket (1), the engagement, centering and holding in place, with the capability of angular orientation, of an anchoring and/or stabilizing pin with fins (3).

The invention relates to a sliding tricompartmental knee prosthesis.

In a well-known manner, this type of prosthesis essentially comprises afemoral implant and a tibial implant. The invention specifically relatesto a tibial implant of the type comprising a metallic socket accepting apolyethylene plate suitably shaped to receive, on sliding, the condylesof the femur.

The tibial sockets on known devices have a stabilizing and/or anchoringpin intended to be impacted in the spongy substance of the proximalextremity of the tibia. These pins are firmly attached, directly orindirectly, to the tibial socket and can have stabilizing fins acting asanti-rotatory devices.

Indirectly attached pins are usually fixed by means of screws under thetibial socket. For example, reference can be made to French Patent Nos.9,103,595 and 9,109,247 and U.S. Pat. Nos. 4,938,769 and 4,944,757.

In each of the above referenced patents, the stabilizing and/oranchoring pin is supported against the lower face of the tibial socket,while one or more screws are inserted from the upper face of the tibialsocket into corresponding fittings in the pin. In some cases, the pincan have a centering head inserted in an opening in the tibial socket.For example, see French patent 9,109,247 and U.S. Pat. No. 4,944,757.

However, it is still necessary in the previously known devices to insertthe pin from the underside of the socket and then to fix it in placefrom above.

It is therefore evident that in all of these previously known devicesthat the fixing in place of the pin is performed from the underside ofthe tibial socket in such a way that it is necessary to firmly attachthe pin to the socket before its impaction.

Given that it is the pin which determines the positioning of the socketrelative to the proximal extremity of the tibia, such previously usedarrangements are not rational in that they do not provide appropriateregard for the quality of the fixing of the device in the patient.

The object of the invention is to remedy these drawbacks in a simple,sure, effective and rational manner. Namely, the current inventionallows for the impaction of the tibial socket in the leg of a patientprior to the introduction of an optional stabilizing and/or anchoringpin. This allows for a final fitting of the device in the patient ratherthan before the impaction process begins, as was previously known.

Under the current invention, a tibial socket has been conceived anddeveloped. The tibial socket has a recess and a protuberance jutting outfrom a lower face of the tibial socket. The protuberance being shaped toact as a pre-anchoring pin to aid in the impaction of the tibial socket.This tibial socket also has a recess of a given shape and section suchthat the engagement, centering and securing of a stabilizing and/oranchoring pin can be accomplished through an upper face of the tibialsocket. Furthermore, the stabilizing and/or anchoring pin optionally hasfins and is capable of angular orientation within the tibial socket.

Advantageously, the protuberance jutting out from the lower face of thetibial socket has a flattened cone-shaped external surface.

To ensure that the stabilizing and/or anchoring pin can be lockedsecurely in place, the pin has a head with a shoulder that cooperateswith a counterboring in the recess in the tibial socket. Suchcooperation allows for the securing of the pin taking into account itsinsertion from the upper face of the tibial socket. Both the head andthe recess cooperating with the head are generally in circular form.

The fins on the stabilizing and/or anchoring pin ensure the rotatorystability of the tibial implant. The fins communicate with traversingslits in the recess of the tibial socket whose number and orientationcorrespond to the number and orientation of the fins on the pin.

According to a further aspect of the invention, the head of thestabilizing and/or anchoring pin has fittings for fixing to the recess.The fittings comprise vertical slits formed around the periphery of thehead for its diametric expansion under the action of a tightening screw.

To ensure the fixing of the tibial socket to the spongy and/orperipheral cortical bone of the tibia, the tibial socket has holes forthe passage of the fixing screws. Thus, the tibial socket may be fixedwhether or not fitted with the stabilizing and/or anchoring pin.

The tibial socket is asymmetric and has a peripheral rim. The peripheralrim is equipped to facilitate the fixing of a polyethylene tibial platesuch that the proper positioning of the tibial plate can be effectedafter the fixing of the socket.

The invention is described below in more detail with reference beingmade to the accompanying Figures.

FIG. 1 is a perspective view showing the main elements of the tibialimplant, which are shown aligned in order of assembly, an example of afemoral implant is also shown;

FIG. 2 is a perspective view, corresponding to FIG. 1 after assembly ofthe components of the tibial implant, which is shown as a three quartersview from above;

FIG. 3 is a similar view to FIG. 2, with the tibial implant shown inthree quarters view from below;

FIG. 4 is a plan view of the tibial socket;

FIG. 5 is a cross section following the line 5.5 of FIG. 4; and

FIG. 6 is a cross section following the line 6.6 in FIG. 4.

The tibial implant comprises a tibial socket (1) accepting apolyethylene tibial plate (2) and a stabilizing and/or anchoring pin(3). The plate (2) of this tibial implant co-operates with all types offemoral implant (F). The tibial socket (1) has an asymmetric shape totake into account the asymmetry existing between the internal andexternal compartments of the tibial head.

According to the invention, the tibial socket (1) has a traversingrecess (1a) shaped so as to allow, from its upper face (1b), theengagement, centering and holding in place of the pin (3).

This recess (1a) is extended by a protuberance (1a1) jutting out fromthe lower face (1c) of the tibial socket (1). This protuberance (1a1) isshaped to act as a stabilizing pin, to ensure, if necessary, the primaryfixing of the tibial socket (1). This protuberance (1a1) has a flattenedcone-shaped extension (1a2). In addition, this protuberance can beextended laterally by ribs for rigidity (1a4) (FIG. 3).

The recess (1a) has an internal counterboring (1a3) for the centeringand support of a head (3a) formed at the upper extremity of the pin (3).

In the example illustrated, the pin (3) has a cylindrical body. In theseconditions, the recess (1a) has a corresponding section. In addition,the head (3a) of the pin (3) has vertical slits (3a1) around itsperiphery. This head delineates a flattened cone-shaped internalcounterboring (3a2) opening up in a threaded hole (3b) for the insertionof a screw (4). This screw (4) has a flattened cone shaped head with asection complementary to the counterboring (3a2) such that, during theaction of inserting the screw into the pin, the screw causes diametricexpansion of the head (3a) of the pin, thereby ensuring its binding tothe tibial socket (1).

The pin (3) has, jutting out from its surface line, radial stabilizingfins (3b). The traversing recess (1a) of the tibial socket (1) has slits(1a5), also traversing, whose number and orientation correspond to thenumber and orientation of the fins (3b) of the pin (3), and thus,cooperate With the fins (3b) during the insertion of the pin (3).

The tibial socket (1) also has holes (1d) for the insertion of spongybone screws (not shown). For example, as shown in FIG. 4, the socket hasfour holes (1d). These holes are shaped to make it possible to embed theheads of the screws, if necessary permitting their angular orientation.

The technical characteristics of the tibial socket (1) are especiallyadvantageous for its impaction.

Firstly, a doctor positions the socket (1), without the pin. Theflattened cone-shaped protuberance (1a1) aids in the primary fixing ofsaid socket, thus permitting perfect periodical support.

Subsequently, the doctor fixes the socket using spongy bone screwsinserted in the holes (1d). It is thus possible to introduce the pinthrough the recess (1a), which also acts as a boring guide. All thatremains to be done is the fixing of the pin to the socket, whichproduces expansion of the head (3a) by means of the screw (4).

It is therefore evident that the introduction of the pin (3) from abovethe socket (1) allows it to be firmly attached to the said socket afterthe latter is correctly impacted. The result is that the pin does notinterfere with the positioning of the socket and therefore the supportsare perfectly respected.

After impaction of the tibial socket and of the pin (3) in the mannerdescribed above, the doctor positions the polyethylene plate in thesocket (1). For this purpose, the socket (1) has a peripheral rim (1e)shaped for the fixing of the plate (2) mainly by snap-fitting. Theshapes and the profiles of the plate (2) are not described becausevarious embodiments are possible. The same applies to the femoralimplant (F).

The constitutive parts of the tibial implant, notably the socket (1) andthe pin (3), can be of any material and can have any type of surfacetreatment.

In an alternative embodiment (non-illustrated), the head of the pinand/or the traversing recess (1a) of the socket is equipped withadditional means allowing the angular orientation of said pin and itslocking in position. For example, these means may comprise a sphericalhead, situated at the level of the head (3a), intended to be inserted inthe opening (1a) of the tibial socket with a complementary sphericalshape.

These arrangements prove to be especially advantageous for replacementprostheses for which quite large pins are used. If the pin isperpendicular to the socket (1b) and if the surgeon tilts the socketbackwards, the pin makes contact with the anterior cortical area. Thispossibility of angular adjustment of the pin relative to the socket thusmakes it possible to align said pin in the axis of the tibial medullarycanal.

The pin (3) can also be covered with a dense, non-osteoconductive,ceramic material whose reabsorption can be controlled by altering thecomposition of said material.

The advantages are apparent from the description; in particular, thefollowing are emphasized and restated:

placement of the pin after impaction of the tibial socket, taking intoaccount its introduction from the upper face of said socket, avoidsadverse effects on the cortical support desired,

ease of impaction,

possibility of equipping the socket with various pin shapes suited tothe pathological case to be treated,

orientation of the pin relative to the tibial socket, notably in thecase of replacement prostheses.

I claim:
 1. A tibial implant for a knee prosthesis comprising:a tibialsocket configured to accept a polyethylene trial plate; and, anelongated pin for anchorage in the bone and for supporting the tibialimplant, said pin terminating at opposite ends wherein a head portion isformed at one end, said head portion having radial stabilizing finsextending outwardly from said pin; said tibial socket having a conicalwall with a recess formed therein defining an internal counterbore andslits formed in said wall wherein said socket is configured to receivesaid head and said stabilizing fins of said pin; said head having athreaded internal counterbore formed therein for accepting a screw andhaving vertical slits formed around said counterbore; said screw havinga flattened cone-shaped head with a section that conmmnicates with saidinternal counterbore such that insertion of the screw into the pincauses diametric expansion of the head which securely and rigidly bindsthe pin to the tibial socket.
 2. The tibial implant of claim 1, whereinthe tibial socket further comprises a protuberance projecting from alower face of said tibial socket at the recess in said tibial socket. 3.The tibial implant of claim 1, wherein the protuberance has a flattenedcone-shaped extension.
 4. The tibial implant of claim 1, wherein therecess and the head are substantially circular in shape.
 5. The tibialimplant of claim 1, wherein the tibial socket has through holes tofacilitate insertion of spongy bone screws for fixing the tibial socket.6. The tibial implant of claim 1, wherein the tibial socket has aperipheral rim; wherein the tibial plate has a peripheral collar; andwherein said peripheral rim engages said peripheral collar for snapfitting of said tibial plate to said tibial socket.